This invention relates to a head feeding mechanism of a magnetic head actuator assembly for use in a linear magnetic tape storage system represented by a DLT (digital linear tape) or an LTO (linear tape open) and, in particular, to a head feeding mechanism capable of simplification of a shape form in the feeding side and improvement of the feeding accuracy thereof.
A linear magnetic tape storage system (magnetic recording/reproducing apparatus) of the type has been developed as a backup for a memory device (e.g. a hard disk) of a computer system. Various types of linear magnetic tape storage systems have already been proposed. For example, a digital linear tape drive as a DLT is disclosed in U.S. Pat. No. 5,862,014.
The digital linear tape drive (which may simply be called “tape drive”) is adapted to receive a tape cartridge having a single reel (supply reel) and contains a take-up reel in the interior thereof. When the tape cartridge is loaded in the tape drive, a magnetic tape is pulled out of the tape cartridge and taken up by the take-up reel through a head guide assembly (HGA). The head guide assembly serves to guide the magnetic tape pulled out of the tape cartridge to a magnetic head. The magnetic head exchanges information between the magnetic tape and the magnetic head. The head guide assembly generally comprises a boomerang-shaped aluminum plate and six large guide rollers each of which comprises a bearing.
The head guide assembly is also called a tape guide assembly and is disclosed, for example, in U.S. Pat. No. 5,414,585. An example of the guide roller is disclosed in Japanese Unexamined Patent Publication No. 2000-100025 (JP 2000-100025 A).
As disclosed, for example, in U.S. Pat. No. 5,793,574, the tape drive is generally comprised of a rectangular housing that has a common base. The base has two spindle motors (reel motors). The first spindle motor has a spool (take-up reel) permanently mounted on the base. The spool is dimensioned to accept a relatively high speed streaming magnetic tape. The second spindle motor (reel motor) is adapted to accept a removable tape cartridge. The removable tape cartridge is manually or automatically inserted into the drive via a slot formed on the drive's housing. Upon insertion of the tape cartridge into the slot, the tape cartridge engages with the second spindle motor (reel motor).
Prior to rotation of the first and the second spindle motors, the tape cartridge is connected to the permanently mounted spool (take up reel) by means of a mechanical buckling mechanism. A number of rollers (guide rollers) are positioned intermediately between the tape cartridge and the permanently mounted spool, and guide the magnetic tape as it traverses at relatively high speeds back and forth between the tape cartridge arid the permanently mounted spool.
The digital linear tape drive having the above-mentioned structure requires a pulling apparatus for pulling the magnetic tape from the supply reel to the take-up reel. Such a pulling apparatus is disclosed, for example, in International Publication No. WO 86/07471. According to WO 86/07471, take up leader means (first tape leader) is coupled to the take-up reel while supply tape leader means (second tape leader) is fixed to the tape on the supply reel. The first tape leader has a mushroom-like tab formed at its one end. The second tape leader has a locking hole. The tab is engaged with the locking hole.
Furthermore, a mechanism for joining the first tape leader to the second tape leader is required. Such a joining mechanism is disclosed, for example, in International Publication No. WO 86/07295.
Japanese Unexamined Patent Publication No. 2000-100116 (JP 2000-100116 A) discloses “Structure of Leader Tape Engaging Part”. In this structure, an end of a leader tape (second tape leader) can be locked to a tape end hooking part of a tape cartridge without requiring a tab projecting on a lateral side of the leader tape.
U.S. Pat. No. 5,857,634 discloses a locking system for preventing the rotation of a take-up reel of a tape drive when a tape cartridge is not inserted into the drive.
On the other hand, an example of the tape cartridge to be received in the digital linear tape drive is disclosed in Japanese Unexamined Patent Publication No. 2000-149491 (JP 2000-149491 A).
U.S. Pat. No. 6,241,171 discloses a tape drive in which a tape leader can be urged from a tape cartridge through a tape path to a take-up reel without using a buckling mechanism or a take-up leader.
The tape drive further comprises a magnetic tape head actuator assembly. The magnetic tape head actuator assembly is positioned between the take-up spool and the tape cartridge along a tape path defined by a plurality of rollers. During operation, the magnetic tape streams back and forth between the take-up spool and the tape cartridge, coming into close proximity to the magnetic head actuator assembly while streaming along the defined tape path. An example of such a magnetic tape head actuator assembly is disclosed in the above-mentioned U.S. Pat. No. 5,793,574.
Referring to FIG. 1, description will be made of the structure of a typical tape drive comprising a magnetic head actuator assembly. FIG. 1 is a plan view of the tape drive in the state where an upper cover is removed.
The tape drive 10 is adapted to receive a removable tape cartridge (not shown) and includes a take-up reel 11 in the interior thereof. The take-up reel 11 may be called a spool. The tape drive 10 comprises a generally rectangular housing (gear chassis) 12 having a common base. The base of the housing 12 has two spindle motors (reel motors) 13 and 14. The first spindle motor 13 has the take-up reel 11 permanently mounted to the base. The take-up reel 11 is dimensioned so as to accept a magnetic tape (not shown) streaming at a relatively high speed. The second spindle motor 14 is adapted to receive the removable tape cartridge. The removable tape cartridge is manually or automatically inserted into the tape drive 10 via a slot 16 formed on the housing 12 of the tape drive 10 along the extending direction of the slot 16.
When the tape cartridge is inserted into the slot 16, the cartridge is engaged with the second spindle motor 14. Prior to rotation of the first and the second spindle motors 13 and 14, the tape cartridge is connected to the permanently mounted take-up reel 11 by means of a mechanical buckling mechanism. A number of rollers (guide rollers) 15 are positioned between the tape cartridge and the take-up reel 11 and guide the magnetic tape as it streams at a relatively high speed back and forth between the tape cartridge and the permanently mounted take-up reel 11.
The housing 12 is made of aluminum die-casting, which is a non-magnetic material. Accordingly, the second spindle motor 14 is covered with a plate of an iron-based magnetic material in order to inhibit magnetic leakage from a magnet (not shown) of the second spindle motor 14.
The tape drive 10 further comprises a magnetic tape head actuator assembly (hereinafter may be simply called “actuator assembly”) 20. The actuator assembly 20 is positioned between the take-up reel 11 and the tape cartridge along a tape path (not shown) defined by the rollers 15. During operation, the magnetic tape streams back and forth between the take-up reel 11 and the tape cartridge, coming into close proximity to the actuator assembly 20 while streaming along the defined tape path.
Next, referring to FIGS. 1 and 2, description will be made of an outline of the actuator assembly 20. As shown in FIG. 2, the actuator assembly 20 comprises the head assembly 30 and the head feeding mechanism 40. And the head feeding mechanism 40 comprises a rotation portion and a linear movement portion moving up and down in a direction of a rotation axis of the rotation portion.
The actuator assembly 20 is disposed on the base of the housing 12 and has a magnetic head assembly 30 moving along and in proximity of a magnetic tape surface. On the base of the housing 12, a guide bar 17 is fixedly mounted to guide the magnetic head assembly 30 moving up and down linearly in a vertical direction or a direction perpendicular to the base of the housing 12.
The magnetic head assembly 30 comprises a magnetic head 31 extending in the vertical direction, a head holder 32 holding the magnetic head 31 on its one side surface (hereinafter may be called “front surface”), and a pair of flexible printed circuits (hereinafter may be abbreviated to “FPC”) 33. The FPCs 33 extend at the opposite side surface (hereinafter may be called “rear surface”) to electrically connect the magnetic head 31 and an external circuit (not shown). By screwing screws 34 to a head lift body 42 of the head feeding mechanism 40 through the screw holes, the head assembly 30 is coupled to the head lift body 42 of the head feeding mechanism 40.
On the rear side of the head holder 32, the head feeding mechanism 40 is disposed with a lead screw 41 having a screw center axis as a rotation center axis extending in the vertical direction. The head lift body 42 is engaged with the lead screw 41 and moves up and down together with the head assembly 30 following the rotation of the lead screw 41.
Next, description will be made of the head feeding mechanism 40 shown in FIG. 2.
The head feeding mechanism 40 comprises the lead screw 41 with an external thread, the head lift body 42, and a backlash preventing mechanism 43 for preventing the backlash of the actuator assembly 20.
The lead screw 41 has a rotation center axis extending in the vertical direction and is provided with a lead screw gear 44 attached to a lower end thereof. The lead screw gear 44 serves to rotate the lead screw 41 around the rotation center axis when it is driven by a driving machine (not shown). The head lift body 42 moves up and down along the rotation center axis following the rotation of the lead screw 41 around the rotation center axis.
The head lift body 42 comprises a base portion 421, a ceiling portion 422, and a semi-cylindrical portion 423. The base portion 421 and the ceiling portion 422 extend substantially in parallel to each other and are spaced in the vertical direction and connected to each other by the semi-cylindrical portion 423. The semi-cylindrical portion 423 has an upright gutter-like shape as a half-split cylinder, which is taken by cutting a hollow cylinder by a plane along the center axis thereof. Accordingly, the head lift body 42 has a generally “I” shape as seen from a lateral side. The head lift body 42 holds the head assembly 30 and moves up and down together with the head assembly 30. In the head lift body 42, the backlash preventing mechanism 43 is arranged inside of the hollow opening of the semi-cylindrical portion 423.
The backlash preventing mechanism 43 includes a pre-load bushing 431 and a pre-load spring 432 of a compression coil spring. The pre-load bushing 431 has an internal thread to be engaged with the external thread of the lead screw 41 when the pre-load bushing 431 is located in the hollow opening of the semi-cylindrical portion 423. The pre-load spring 432 is disposed in a compressed state between the head lift body 42 and the pre-load bushing 431.
The lead screw gear 44 is fixed to the lower end of the lead screw 41 and serves to rotate the lead screw 41 around the rotation center axis when it is driven by a driving machine (not shown). The lead screw 41 is engaged with an internal thread 451 of a nut 45 mounted on the head lift body 42. Accordingly, the rotation of the lead screw 41 around the rotation center axis thereof moves the head lift body 42 in the vertical direction coincident with the extending direction of the rotation center axis, in cooperation with the pre-load bushing 431.
Next, description will be made of the structure of the head lift body 42 more in detail.
The head lift body 42 includes the nut 45, which has the internal thread 451 to be engaged with the lead screw 41, a plain or sliding bearing 46 (will later be described), and a guide portion 47 (will later be described).
As described above, the head lift body 42 has a main portion composed of the base portion 421 defining a lower end surface, the ceiling portion 422 defining an upper end surface, and the semi-cylindrical portion 423 with the hollow opening. Each of the base portion 421 and the ceiling portion 422 has a pair of peaks extending outward from opposite sides of the semi-cylindrical portion 423. As seen in a direction perpendicular to the extending direction of the peaks, i.e., as seen from the lateral side, the head lift body 42 has a generally “I” shape. The base portion 421 and the ceiling portion 422 have circular openings formed at positions corresponding to the hollow opening of the semi-cylindrical portion 423 to form the plain or sliding bearings 46, respectively, which receive the lead screw 41 inserted therethrough.
At the position of the above-mentioned circular opening to receive the lead screw 41 inserted therethrough and in the hollow opening of the semi-cylindrical portion 423, the base portion 421 is provided with the nut 45 having the internal thread 451 to be engaged with the lead screw 41. In the figure, the nut 45 is fixedly mounted on the upper surface of the base portion 421 in the hollow opening of the semi-cylindrical portion 423. Alternatively, the nut 45 may be integrally molded, for example, embedded in the base portion 421 at that position.
One of the peaks of the base portion 421 laterally extends as an arm to the length longer than the other peak and has the guide portion 47 of a generally “U” shape at its end. The guide portion 47 is fitted and attached to the guide bar 17 illustrated in FIG. 1 so as to be slidable in the vertical direction. The guide portion 47 serves to prevent the rotation of the head lift body 42 around the rotation central axis.
The ceiling portion 422 has a pair of screw holes in its peaks engaged with the screws 34, respectively. By screwing the screws 34 into the screw holes, the head assembly 30 is fixed to the head lift body 42. The hollow opening of the semi-cylindrical portion 423 serves to receive the backlash preventing mechanism 43 comprising the pre-load bushing 431 and the pre-load spring 432.
That is, the backlash preventing mechanism 43 comprises a combination of the pre-load bushing 431 and the pre-load spring 432, and serves to prevent backlash of the actuator assembly 20.
The pre-load bushing 431 comprises a cylindrical portion with an internal thread formed on its inside surface, an external annular receiving portion, and a semi-cylindrical wall portion. The external annular receiving portion extends radially outward at the lower end of the cylindrical portion to serve as a stopper for the pre-load spring 432. The semi-cylindrical wall portion extends upward from an outer periphery of the receiving portion in an area corresponding to an approximately half circle. Accordingly, a semi-annular gap is formed between the cylindrical portion and the semi-cylindrical portion. As shown in FIG. 4, the pre-load spring 432 is partially received in the semi-annular gap and is disposed in a compressed state between the annular receiving portion of the pre-load bushing 431 and the lower surface of the ceiling portion 422 of the head lift body 42. Furthermore, both ends of the semi-cylindrical wall portion of the pre-load bushing 431 inhibit the rotation of the pre-load bushing 431 by engagement with edges of the semi-cylindrical portion 423 when the pre-load bushing 431 is mounted into the head feeding mechanism 40.
The pre-load spring 432 is a compression coil spring. By mounting the pre-load spring 432, the pre-load bushing 431 is continuously applied with a downward pressing force along the rotation center axis of the lead screw 41, while the head lift body 42 is continuously applied with an upward pressing force along the rotation center axis of the lead screw 41. As the guide portion 47 is integrally formed with the head lift body 42, the guide portion 47 is continuously applied with the upward pressing force along the rotation center axis of the lead screw 41, also.
Accordingly, the above backlash preventing mechanism 43 is capable of preventing backlash between the lead screw 41 and the head lift body 42 during movement following the rotation of the lead screw 41.
The head feeding mechanism 40 described above is insufficient in accuracy for feeding the head lift body 42 to the direction of the rotation axis of the lead screw 41 during movement following the rotation of the lead screw 41. This causes some trouble to impede the magnetic head 31 to accurately trace each track on the magnetic tape.
The reason is that the external thread of the lead screw 41, the tooth of the lead screw gear 44, and the internal thread 451 of the nut 45 are different from each other in shapes and accuracy. Accordingly, positioning of the magnetic head 31 moved cannot be performed at same spaces.
Recently, it has been attempted to increase a number of tracks for increase of storage capacity of data on a magnetic tape and it is, therefore, required to make tracks with narrow and same spaces between the tracks. Accordingly, it could not avoid that any off-track occurs because of some margin of error during reproducing data from the magnetic tape which records the data at same track spaces.